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Old 27th October 2004, 07:38 PM   #1
morbo is offline morbo  Canada
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Default New nearfield 'reference' system design

I've decided that I've been doing too much theorizing and not enough DIYing lately, and under the guise of spending more time on hobbies to relax and bring my blood pressure down, I'm going to build something. The concept is a reference (personal, not absolute) nearfield system. I don't want to start referring to them as 'computer speakers', as that seems to subconsciously lower the expectations, but essentially these will be 20" tall, 6-8" wide, 20" deep desktop monitors. First the parameters and goals for the system:


Fixed Parameters:

1. These speakers will be used exclusively in nearfield, ie on a desktop 1-2.5 feet from the listening position, flanking a computer monitor.

2. These speakers will be listened to on axis 90 % of the time.

3. These will eventually be mated to dual ported 12" subs good to ~ 25hz on the low end, but will need to be crossed below 100hz, prefereably ~ 50-60hz.

4. I have limited measurement capability, tools, woodworking skills, and money



Priorities:

1. Imaging - After hearing the little TB 871s in the nearfield, I know what kind of imaging is possible in this configuration and frankly am enchanted by it. So within reason, imaging trumps all else in this design.

2. Flat frequency response - These don't need to be as flat as studio monitors, but since it is meant to be a reference, even and balanced sound is important to me.


Here's how I plan to go about this:

The design will be essentially an assisted wideband speaker. A 2-way using the TB 871 (which I know and love, plus have a pair to use already) as a widerange, with a bass section crossed in around 200hz. I gave a lot of thought to this and given that I have no proper measurement equipment, an active 2-way crossed outside of the vocal range seems like the most foolproof way to go about this. Beyond this, the upgrade path is very nice, with very easy mixing/matching of drivers, and a Behringer DCX, DEQ, and proper measurement setup on the distant horizon. Plus I think I will learn a lot more from this than from building someone else's design or kit, which I've done numerous times. I'm sure I won't get quite as good a result, but at the very least I'll get a lot of hands on experience, and if I can find a well behaved pair of drivers that integrate well with such simple filters, then all the better. Finally, I have other drivers coming soon (CSS 4.5", Seas tweeters) and this setup will let me do a lot of experimenting with them, as well as letting me do direct comparisons to the other drivers.

My hope is that using the 871 from 200hz-20 will retain most of the great coherence and imaging I get using them standalone, and that releiving them from making bass will clean up their sound at higher levels. I will be using the Behringer CX2310 as a crossover for this system. It uses 24db/oct slopes, so I will start with a 24db/oct lo/hipass @ 200hz and tweak from there.

The 871 will be in its own enclosure (I already have one, so no woodworking!) sitting on top of the woofer box. I have also given some thought to making it diploe and crossing higher, but I suspect that the narrow baffle (6-9" or so) would cause it to roll off very high.


For the bass section, I am a little torn. The low cost choice is the Hivi M4n, little brother of the M8n that is so well regarded. A pair of these should provide decent sealed bass and extend fairly low. Sure they will have limited output, but in the nearfield this shouldnt be that big a problem. The downside is I can't find any information about these, and few people seem to have used them. The Qts is very high, I'm not sure if this is a problem, but being that I like closed speakers with a q around .7, the fact that I can't get these to model at less than q=1.1 or so is a little concerning. The upside is they are so cheap that I could be the first without TOO much damage to the pocketbook I can get the 4 of them for about $50 CDN. The higher cost choice is to go whole hog and use the new 7 or 8" Dayton reference driver in a ported box. I'm sure the bass performance will be amazing with these, with their very low distortion below 100hz they seem like a great choice. However the cost is more than 2x of the hivi drivers... Then again, if I order the hivis, and they turn out not to be suitable, I still have to order the RS and am out even more money. This is the big decision I'm left with.


Any comments on this system or my concept would be very welcome!
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Old 27th October 2004, 08:11 PM   #2
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I run 17x6x12 satellites in mtm config, assisted by two isobarik 12'" subs powerfull enough to fill a 24x21' living room to live concert levels.
Your "nearfield " size seems to be a serious overkill, and the bass from a 12" woofer is likely to permanently damage your eardrums at any slightly elevated levels.
I run my system activ using the behringer dcx and deq 2496, to two bryston 4b (woofer and midbass) and one 2b (tweeter).
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Old 27th October 2004, 09:05 PM   #3
morbo is offline morbo  Canada
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Thanks for your comment. I'm not going to play at extreme volumes or anything, the 12" sub will be under the desk or to the side of it. Just because I could play it really loud doesnt mean I have to, and it seems to me that this will keep all the drivers operating under very good control, no high excursions required from any element of the system.

Really, the subwoofer(s) are not a major element of the system here. I just happened to have 2 12" drivers sitting idle, and since I'm attempting a personal reference, why not make it flat to 25 hz, since I have all the parts to do so anyway? I understand maybe its overkill, but I have the stuff lying around anyway, I'm just trying to maximize what I can do with what I have.
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Old 27th October 2004, 09:26 PM   #4
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Ive also been thinking about using the 871's in a open baffle config for computer speakers. I'm thinking I may have found a way to use up all of the 10'' circles I have cut from my two 6x10'' line arrays. I have the same concern about them rolling off too high with a narrow baffle, but the good side is they have a qts near .6
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Old 27th October 2004, 10:13 PM   #5
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If you are going to build subs anyway, why build woofers at all? What kind of 12" drivers do you have? Also, if you are going to spend all those bux on crossovers etc, wouldn't it make sense to use a better driver than the TB? Maybe one of the better Fostexes (Fostices?) or a JX92S? I assume those are better. They cost more. :-)
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Old 27th October 2004, 10:27 PM   #6
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@Dave Jones: you know what - i had the same driver config builld with dynaudio drivers, and then for fun with vifa speaker - at 1/4 the price. I still run and prefer the vifas. As a penalty the dynaudios burned down with my shop after i had spent about 15 hours on seven coats of black paint...
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Old 27th October 2004, 10:29 PM   #7
morbo is offline morbo  Canada
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Quote:
If you are going to build subs anyway, why build woofers at all?
Because the drivers are of fairly low quality, and I'd really rather use them only as subwoofers, ie below 50hz if possible. And because the 871 doesnt sound great trying to reproduce bass below about 120hz. They are Hifonics Olympian Warriors that I bought from Stryke many years ago. They are car audio woofers, about 9mm xmax, in a sealed box F3 of around 49hz, in a big ported box F3 around 25hz. These are not great subs at all, but used as reinforcement for the very lowest frequencies, they should work fine. I am really after quality here not quantity, and I have zero confidence that these woofers would sound good crossed above 100hz, at least not up to par with what I'm hoping to accomplish. Also, I couldn't fit a decent sized enclosure using them on my desk

Quote:
Also, if you are going to spend all those bux on crossovers etc, wouldn't it make sense to use a better driver than the TB? Maybe one of the better Fostexes (Fostices?) or a JX92S? I assume those are better. They cost more. :-)
Well, the crossover will run me ~$100. The driver cost for the woofers will vary between $50 (2x Hivi) and $100 (1x RS). Total cost either way stays under $200 CDN, which is about all I have disposable ATM. Like I said, I already have the TB and the 12" woofers, so they are free. Now, even assuming that the Jordans or Fostexes are a real improvement over a filtered 871, they triple the cost of the project. One of the nice things about this design is that I could easily upgrade to another widerange driver down the road, but I wouldnt't shell out $200 per/driver for Jordans without A/Bing them with my the little TBs first. Whether they would be better or not is a moot point anyhow as upgrading them takes me well over budget. I have at most $200 to spend, and I want to do the best I can with that. Besides that, when operating within its limits, I think the TB sounds great.
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Old 29th October 2004, 03:59 PM   #8
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Bump because I am also interested in people's suggestions on this, and to see if morbo has made a decision.

I've also been looking at a pair of small 871-based desktop speakers with additional woofer(s) to extend the FR down to a more reasonable frequency for crossing to a sub. I've toyed with the idea of using TB's baby 4" woofer, the 992S, but I'd prefer to use a passive crossover and the 992S has a nasty peak around 2500 Hz that has my limited (well, non-existent) crossover experience frightened. The little Hi-Vi woofers might be better suited in that regard. And I want to keep the box width down, if possible just expanding on Zaphoid's work with the 871 notch filters and compact boxes - just a taller, compartmentalized version of the .1 cu ft box is how I imagine it.
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Old 30th October 2004, 01:20 PM   #9
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Morbo, this is a very intesting project. Are you going to be playing compressed music on it? If this is so, you probably want speakers that are fairly forgiving.

I'm also impressed with the 871 and CSS 4.5" driver, the latter in particular. The off axis response and the flat freq response are very impressive. Further this driver has very low distortion. It seems to me that it has some features not often found in one driver - widerange, very low distortion, very high xmax, very smooth on and off axis response, and it is probably a forgiving driver. I'm not keen on metal cone drivers for music that isn't "audiophile." I now prefer drivers that aren't high resolution - paper, poly, etc.

If you go with fairly sophisticated eq units like behringer ultradriver / deq, then one thing you can do which is interesting is correct the recording. I'm convinced that my enjoyment of music will go up when I get my system set up like this and create custom eq settings with ultracurve for different types of music, possibly even for individual cds or bands, etc.

With the size you mentioned you can do some interesting things with the box. I have heard some say that a fullrange driver in an inverted horn enclosure (like B&W nautilus and Norh) that you can get spectacular imaging. I believe it has to do with getting closer to a point source and minimising box coloration. You might find some of the technical info on the development of the Nautilus enclosure interesting - it's on their site and you can download PDF files. I would look into designing an enclosure based on these principles for the midrange driver.

If you use the CSS 4.5" driver then you could cross at say 80 Hz to a sub. Seems a shame to use a low quality sub. Granted you have some already, but if you do upgrade then you can get much lower distortion. I was looking at some sub measurements and the distortion in a sub can be extreme, even in some very expensive subs ~ 36%!!! I hate to think what you get in cheap subs or woofers. The Adire extremis looks like a great driver to use as a woofer, and the fact that it is shielded is a huge bonus.

What are you thinking of using for a tweeter? I'd be looking at one with a very small face plate. Chances are you will want to cross high, which wants a close driver to driver distance. Vifa and Seas have neodymium tweeters that would suit.
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Old 31st October 2004, 02:49 AM   #10
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Default HI Morbo :)

I have jordans in ceramic pots and they are supurb! my best friend needed HT , so we ordered 6 871s and put them in 2 liter pots sealed.sub xos at 200, its a jbl 8 inch car woofer in a toob that i had laying around . In his large room they are astounding! but no heavy HT type bass of course. they sounded sooooo good i brought 2 home to ab with my jordans! BIG mistake, the jurdans slaughtered them as you would expect for $100 more each . returned them to his house and they sounded supurb again. i go over often and he always playes them and i thuroughly enjoy them for what they are! you wont be sorry you used then but a sub or two is mandatory 2 8" subs would be perfect notice i listen exclusively at ~40" nearfield, and he is far field in a BIG room and it still impresses me. highly recomended as bang for buck kings u might want to just build zaphoids sys. you could do much worse
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